/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.flink.api.table.trees

/**
 * Base class for tree analyzers/transformers. Analyzers must implement method `rules` to
 * provide the chain of rules that are invoked one after another. The tree resulting
 * from one rule is fed into the next rule and the final result is returned from method `analyze`.
 */
abstract class Analyzer[A <: TreeNode[A]] {

  def rules: Seq[Rule[A]]

  final def analyze(expr: A): A = {
    var currentTree = expr
    for (rule <- rules) {
      var running = true
      while (running) {
        val newTree = rule(currentTree)
        if (newTree fastEquals currentTree) {
          running = false
        }
        currentTree = newTree
      }
    }
    currentTree
  }
}
